Fusing apparatus

ABSTRACT

Apparatus is provided for fusing a toner image to a sheet comprising a hot roll fuser in which the heated roll is provided with a thin resilient coating and the other roll is elastic and deformable when in pressure contact with the heated roll. The sheet is fed through the hot roll fuser with the toned image contacting the heated roll and an auxiliary heating device is positioned in the sheet path before the hot roll fuser so that the non-image side of the sheet is heated by the auxiliary heating device to a temperature below the temperature at which damage to the sheet occurs and driving the heated roll at a speed so that the coating is in contact with the toner image a time sufficient to fuse the powder image to the sheet without offsetting to the coating.

[ Jan. 21, 1975 1 FUSING APPARATUS Bader S. Kudsi, San Jose, Calif.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

221 Fi1ed: Dec. 19, 1913 211 Appl. No.: 426,383

[75] Inventor:

[52] US. C1 432/60, 432/228, 219/216 [51] Int. Cl 603g 13/20 [58] Field of Search 432/59-60,

[56] References Cited UNITED STATES PATENTS 3,207,129 9/1965 Limberger 219/216 3,291,466 12/1966 Aser et a1. 432/60 3,409,280 11/1968 Springett 432/60 3,449,546 6/1969 Dhoble 219/216 3,449,548 6/1969 Adamek et a1. 219/216 3,452,181 6/1969 Stryjewski 432/60 3,498,596 3/1970 Moser 432/60 3,517,164 6/1970 Huggins et a1. 219/216 3,539,161 11/1970 Byrne 432/60 3.700218 111/1972 Laisncy ..432/6(1 Primary Examiner1ohn .1. Camby Assistant Examiner-Henry C. Yuen Attorney, Agent, or Firm-Otto Schmid. Jr.

[57] ABSTRACT Apparatus is provided for fusing a toner image to a sheet comprising a hot ro1l fuser in which the heated roll is provided with a thin resilient coating and the other roll is elastic and deformable when in pressure contact with the heated roll. The sheet is fed through the hot r011 fuser with the toned image contacting the heated roll and an auxiliary heating device is positioned in the sheet path before the hot r011 fuser so that the non-image side of the sheet is heated by the auxiliary heating device to a temperature below the temperature at which damage to the sheet occurs and driving the heated roll at a speed so that the coating is in contact with the toner image a time sufficient to fuse the powder image to the sheet without offsetting to the coating.

6 Claims, 5 Drawing Figures PATENIEDJMI ms CONTROL S85E11 (f 2 MEANS HOT ROLL TEMPATURHF) FORCE (LBS PER mom F IG.2

PATENTEU- 1 5 SHEET 2 0F 2 T 425 HOT RDLL TEMPATURHF) PAPER TEMPATURHF) FIG.3

FUSING APPARATUS BACKGROUND OF THE INVENTION This invention relates to a heat fusing apparatus for use in fixing images of a resinous powder to a support such as paper and more particularly to fusing apparatus in which the heating element is brought into contact with the image to be fixed after the paper has been preheated with an auxiliary heating device.

One technique for fusing a powder image to paper is to have direct physical contact between a hot surface such as a heated roller and the powder image so that the resin is heated to the necessary temperature for fusing. However, this method has the disadvantage that offset may occur. Offset is caused by part of the image sticking to the surface of the heated roller so that, when the next sheet comes into contact with the roller, the image partially removed from the first sheet is transferred to the second sheet. Thus, the second sheet will be an unacceptable copy. This offset problem has been overcome in commercial machines by fabricating the outer surface of the heated roll with a material such as Teflon; however, this apparatus requires that the heated roll be continuously coated with an offset-preventing liquid such as silicone oil during opera tion. There has been developed a heated roll coated with a resilient material such as silicone rubber which when operated with a deformable backup roll will produce offset-free operation over a particular range of temperature and pressure without the use of an offsetpreventing liquid such as silicone oil. However, in a system which utilizes high process speeds in which the components of the system are required to have mainte nance-free operation for a long period of time. the prior art apparatus is no longer suitable. The prior art apparatus which utilizes an offset-preventing liquid must have the reservoir of offset-preventing liquid replenished periodically which is unacceptable in such a system. The hot roll fuser with a silicone rubber coating requires high temperatures on the surface of the heated roll to get sufficient heat into the paper to fuse the toner material at the high process speeds. The high temperature severely limits the life of the silicone rubber coating on the heated roll so that the maintenance requirements for the system cannot be met by this ap' paratus. On the other hand, an attempt to lower the operating temperature results in either offset or poor fuse quality or both.

SUMMARY OF THE INVENTION It is therefore the principle object of this invention to produce a fuser apparatus which is capable of fusing images without offset at a high process speed and which produces maintenance-free operation for long periods of time.

Briefly, according to the invention, apparatus is provided for fusing a resinous powder image to a substrate comprising a hot roll fuser which utilizes a resilient coating on the heated roll and another roll that is elastic and deformable when in pressure contact with the heated roll. An auxiliary heating device is positioned in the path of the substrate so that the substrate is heated by said auxiliary heating device to a temperature below the temperature at which damage to the substrate occurs and the rolls are driven at a speed so that the coating is in contact with the toner image a time sufficient to fuse the powder image to the coating.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an electrophotographic apparatus embodying the present invention;

FIG. 2 is a graph showing the relationship between hot roll temperature and the meshing force of the fuser rolls;

FIG. 3 is a graph showing the relationship between hot roll surface temperature and paper temperature relative to offset zones;

FIG. 4 is a side view of the fuser station;

FIG. 5 is a view partially in section showing an alternate embodiment of the auxiliary heating device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrophotographic apparatus embodying the invention is shown in FIG. 1. The electrophotographic apparatus comprises a rotatable drum 1 which carries around its periphery an electrophotographic photoconductive member upon which is directed an image which it is desired to be produced on continuous form web 6. The surface of the photoconductor is uniformly charged to a predetermined polarity by corona discharge device 2. The charged surface is exposed to a light image at the forms flash station 3 and/or exposure station 4 to produce a latent electrostatic image. The latent electrostatic image is developed by a suitable development unit 5 at which a toner carrier mixture is cascaded across the electrostatic image on the surface of the photoconductor as is known in the art. The toner has a charge opposite from the polarity of the electrostatic image charge and so is attracted to the drum sur face to render the image visible. The toned image is transferred to continuous form sheet 6 with the aid of transfer corona unit 7. The transfer corona unit sprays ions on the backside of sheet 6 of a polarity opposite that of the toner, thereby attracting the toner image from drum I to sheet 6. After the corona transfer, the paper 6 is separated from the drum and fed past a fusing station 8 which serves to fuse and permanently fix .the toner to the paper. Since transfer of all the image toner is not usually accomplished, residual toner usually remains on the drum surface after a transfer operation. At the cleaning station the photoconductor is exposed successively to an erase lamp 9, a pre-clean corona l0 and a rotating cleaning brush 11. The erase lamp discharges the photoconductor and the pre-clean corona produces a charge so that the residual image toner is attracted electrostatically to the cleaning brush which sweeps the toner from the photoconductor surface. This operation completes the cycling of the drum for producing the desired image. Control means 14 is provided to supply electrical control signals to coordinate the operation of all components of the system. In this manner, the position of the image on the drum can be coordinated so that the proper action takes place at the stations around the drum at the proper time. In addition, control means 14 may also provide temporary storage for image data supplied to exposure station 4 if desired.

According to the present invention, the fusing station 8 comprises a hot roll fusing device 20 and an auxiliary heating device 22. In the embodiment of the invention shown in the drawings, hot roll fuser means 20 comprises a heated member 24 in the shape of a roller and includes a heat conducting tubing 26 having infra-red lamps 28 disposed therein and with a deformable layer 30 of an insulating high temperature material such as one comprising silicone rubber. The wattage of lamps 28 will vary depending upon the speed of the web through the fusing station and the desired temperature for the hot roll surface temperature. Tube 26 is made from a suitable material such as copper or aluminum which is a good heat conductor. However, since high temperature materials such as silicone rubber are heat insulating materials, the thickness of the deformable layer 30 must be kept thin since heat conductance decreases with increased thickness and in a practical embodiment, this thickness would normally be mils or less. The backup element 32 is also in the shape of a roller and the roller is pushed against the heated roll 24 with a meshing force supplied in the illustrated embodiment by cam means 34. The backup element is also formed of a high temperature elastomer 36 such as one comprising silicone rubber.

Heated roll 24 is driven by a suitable motor 5 through suitable belts or gears, shown clotted in the drawings, and when backup roll 32 is meshed with the heated roll, the pressure causes the paper web 6 to be driven through the hot roll fuser and to fuse and permanently fix the toner image to sheet 6. Suitable signals to control the drive of hot roll fuser are provided by control means 14.

It can be seen by referring to FIGS. 2 and 3 that a meshing pressure for the fuser rolls and a surface temperature for the heated roll must be chosen based on the properties of the materials and the maintenance requirements for the system. FIG. 2 shows the relationship between hot roll temperature and roll meshing force with a constant paper temperature at the input to the hot roll fuser for a typical fuser which has a thin coating of a resilient material such as silicone rubber on the hot roll and a backup roll that is resilient and deformable when in pressure contact with the hot roll.

FIG. 3 shows the relationship between hot roll tem perature and the paper temperature at the input to the hot roll fuser with a constant meshing force for a fuser such as that described relative to FIG. 2. In FIG. 3 the area to the left of line 38 represents an area of cold offset whereas the area to the right of line 40 represents an area of hot offset. The line 42 represents a plot of the typical characteristics of a hot roll fuser in the desired operating range. The operating range, depending upon the material selected, may go in excess of 500; however, there is an inverse relationship between the operating temperature of the hot rolls and the lifetime of the material in the fuser environment for layer 30. It can be seen that it is desirable to operate the hot roll at as low a temperature as possible; however, lowering the hot roll temperature beyond a specified temperature produces cold offset. The hot offset part of the curve comes into the operation of the system when one considers that web 6 is operated in a start/stop mode. Although the pressure is removed from the hot roll fuser and the lamps 28 are turned off, there is still a possibility that the image toner in an area that has been stopped will produce hot offset when the fuser is restarted.

An auxiliary heating device 22 is positioned along the path of travel of web 6 prior to the entry of web 6 into the hot roll fuser. Auxiliary heating device 22 is positioned so that the back (non-image side) of web 6 intimately contacts the surface of auxiliary heating device 22. By reference to FIG. 3, it can be seen that the addition of the auxiliary heating device provides another variable which can be utilized in the design of a fusing station to vary the paper temperature at the input to the hot roll fuser up to an upper limit which is the temperature at which paper begins to discolor after prolonged exposure to that temperature. Auxiliary heating device 22 comprises a plurality of heating elements 46 suitably placed in a heat conductive body member 48 so that the surface 42 can be maintained at a predetermined temperature by controlling by a suitable thermostatic control circuit (included in control means I4) the heat generated by elements 46. The tension of the web produced by the drive of the hot roll fuser 20 and the tractor drive means 50 produces intimate contact between the backside of web 6 and the auxiliary heating device surface 42 in the embodiment shown in FIG. I. In this manner, the temperature of the paper as it enters hot roll fuser 20 can be closely controlled to produce fusing of toner to the web without offset to the heated roll. This operation also does not produce the hot offset during start/stop operation of the electrophotographic apparatus.

The drive to hot roll fuser 20 and tractor means 50 is controlled by suitable signals from control means 14. In addition, the pressure between rolls 30 and 32 is controlled by arm 54 to which shaft 35 is attached. Arm 54 is pivoted at point 52 so that rotation of shaft 56 to a predetermined angular position drives cam means 34 as shown in FIG. 4 to produce the predetermined pressure between rolls 30 and 32.

An alternate embodiment of auxiliary heating means 22 is shown in FIG. 5. In this embodiment, the web is maintained in intimate contact with auxiliary heating means by a series of holes 58in member 60. A manifold is provided below member 60 and vacuum is produced at vacuum inlet 62 of sufficient level to pull web 6 into intimate contact with member 60. In this manner, all areas of web 6 are heated to substantially the same tem perature. In the event an air bubble occurred between member 60 and web 6, the area encompassed by the bubble would not be heated to the chosen level and this may result in cold offset in that area of the sheet when the sheet is passed through hot roll fuser 20.

In one specific embodiment a hot roll fuser was used which had a silicone rubber coating on the hot roll about l0 mols thick. The hot roll was operated at a temperature of about 3 l5F., the auxiliary heating device was operated at a temperature of 315F. and a pressure of 12 pounds per inch was produced between the hot roll and the backup roll. This apparatus produced consistently good fusing for several million cop ies at a process speed in excess of 30 inches per second without replacing the hot roll and without the use of an offset preventing material such as silicone oil.

Similar apparatus was also successfully operated with the hot roll temperature at about 320F., the auxiliary heating device at about 220F. and a pressure between the hot roll and the backup roll of 30 pounds per inch. Note from FIG. 2 that selection of a higher meshing force for the rolls has the effect of shifting the corresponding plot for the relationship shown in FIG. 3 to a lower hot roll temperature. The selection of the appropriate operating environment can be made by a consideration of all the factors such as the materials being used and other related factors.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. In an electrophotographic apparatus, a fusing apparatus for fixing a resinous powder image to a substrate as said substrate is moved over a predetermined path comprising:

hot roll fuser means comprising first and second rotatable members through which said substrate, carrying the powder image, passes and comes into contact with said first member, said first member having a relatively thin resilient coating surrounding a heat conducting support member, said second member being elastic and deformable by said first member when in pressure contact with said first member;

heating means disposed within said support member for heating the outer surface of said resilient coatmg;

pressure means for applying a meshing force between said members;

an auxiliary heating device having means to maintain the substrate in continuous contact over a substantial length with the non-image side of said substrate in said predetermined path prior to said hot roll fuser means, said auxiliary heating device having a primary source of heat comprised therein and being adapted to produce heat at a level at which substantial heating of the resinous powder results but below the level at which said substrate is damaged by continuous exposure to said heat level; and means for rotating said members at a speed so that the powder image is in contact with the coating for a time sufficient to transfer sufficient heat to the powder image in combination with the heat supplied to the resinous powder by said auxiliary heating device to raise the resinous powder to a temperature capable of fusing said powder image to said substrate without offsetting to the coating.

2. The apparatus according to claim 1 wherein said substrate is a continuous web of paper.

3. The apparatus according to claim 1 additionally comprising control means, said control means producing control signals to operate said means for rotating said members in a start/stop mode.

4. In an electrophotographic apparatus, a fusing apparatus for fixing a resinous powder image to a substrate as said substrate is moved at a predetermined process speed over a predetermined path comprising:

hot roller fuser means comprising first and second rotatable members through which said substrate, carrying the powder image, passes and comes into contact with said first member, said first member having a relatively thin resilient coating surrounding a heat conducting support member, said second member being elastic and deformable by said first member when in pressure contact with said first member; heating means disposed within said support member for heating the outer surface of said resilient couting to a predetermined temperature; pressure means for applying a meshing force between said members, said meshing force and said predetermined temperature being insufficient to produce fusing without offset at said predetermined process speed; an auxiliary heating device having means to maintain the substrate in continuous contact over a substantial length with the non-image side of said substrate in said predetermined path prior to said hot roll fuser means, said auxiliary heating device having a primary source of heat comprised therein and being adapted to produce heat at a level at which substantial heating of the resinous powder results but below the level at which said substrate is damaged by continuous exposure to said heat level; and means for rotating said members at a speed so that said substrate is driven through said members at said predetermined process speed so that the powder image is in contact with the coating for a time sufficient in combination with said auxiliary heating device and said meshing force to transfer sufficient heat to the powder image in combination with the heat supplied to the resinous powder by said auxiliary heating device to raise the resinous powder to a temperature capable of reliably fusing said powder image to said substrate without offsettting to the coating. 5. The apparatus according to claim 4 wherein said substrate is a continuous web of paper.

6. The apparatus according to claim 4 additionally comprising control means, said control means producing control signals to operate said means for rotating said members in a start/stop mode. 

1. In an electrophotographic apparatus, a fusing apparatus for fixing a resinous powder image to a substrate as said substrate is moved over a predetermined path comprising: hot roll fuser means comprising first and second rotatable members through which said substrate, carrying the powder image, passes and comes into contact with said first member, said first member having a reLatively thin resilient coating surrounding a heat conducting support member, said second member being elastic and deformable by said first member when in pressure contact with said first member; heating means disposed within said support member for heating the outer surface of said resilient coating; pressure means for applying a meshing force between said members; an auxiliary heating device having means to maintain the substrate in continuous contact over a substantial length with the non-image side of said substrate in said predetermined path prior to said hot roll fuser means, said auxiliary heating device having a primary source of heat comprised therein and being adapted to produce heat at a level at which substantial heating of the resinous powder results but below the level at which said substrate is damaged by continuous exposure to said heat level; and means for rotating said members at a speed so that the powder image is in contact with the coating for a time sufficient to transfer sufficient heat to the powder image in combination with the heat supplied to the resinous powder by said auxiliary heating device to raise the resinous powder to a temperature capable of fusing said powder image to said substrate without offsetting to the coating.
 2. The apparatus according to claim 1 wherein said substrate is a continuous web of paper.
 3. The apparatus according to claim 1 additionally comprising control means, said control means producing control signals to operate said means for rotating said members in a start/stop mode.
 4. In an electrophotographic apparatus, a fusing apparatus for fixing a resinous powder image to a substrate as said substrate is moved at a predetermined process speed over a predetermined path comprising: hot roller fuser means comprising first and second rotatable members through which said substrate, carrying the powder image, passes and comes into contact with said first member, said first member having a relatively thin resilient coating surrounding a heat conducting support member, said second member being elastic and deformable by said first member when in pressure contact with said first member; heating means disposed within said support member for heating the outer surface of said resilient coating to a predetermined temperature; pressure means for applying a meshing force between said members, said meshing force and said predetermined temperature being insufficient to produce fusing without offset at said predetermined process speed; an auxiliary heating device having means to maintain the substrate in continuous contact over a substantial length with the non-image side of said substrate in said predetermined path prior to said hot roll fuser means, said auxiliary heating device having a primary source of heat comprised therein and being adapted to produce heat at a level at which substantial heating of the resinous powder results but below the level at which said substrate is damaged by continuous exposure to said heat level; and means for rotating said members at a speed so that said substrate is driven through said members at said predetermined process speed so that the powder image is in contact with the coating for a time sufficient in combination with said auxiliary heating device and said meshing force to transfer sufficient heat to the powder image in combination with the heat supplied to the resinous powder by said auxiliary heating device to raise the resinous powder to a temperature capable of reliably fusing said powder image to said substrate without offsettting to the coating.
 5. The apparatus according to claim 4 wherein said substrate is a continuous web of paper.
 6. The apparatus according to claim 4 additionally comprising control means, said control means producing control signals to operate said means for rotating said members in a start/stop mode. 